Rhizome weight and bioactive compounds of Dioscorea birmanica under different shading

Abstract

The rhizomes of the medicinal plant Dioscorea birmanica Prain & Burkill [Dioscoreaceae] are used in Thai traditional medicine for the treatment of cancer. The ethanolic extract of D. birmanica rhizome exhibited high cytotoxic activity against lung, colon and breast cancers [1]. Diosgenin 3-O-α-L-rhamnopyranosyl (1→2)-β-D-glucopyranoside or prosapogenin A of dioscin (DBS1) isolated from D. birmanica rhizome showed high cytotoxic activity against lung cancer but was less toxic against normal lung cells [2]. The rhizomes are typically collected from the forest and cultivation methods to produce rhizomes for medicinal use are still limited. Therefore, rhizome weight and bioactive compounds of D. birmanica under different shading were examined. The plants were grown in plastic pots under 0%, 50% and 70% shading and the rhizomes were harvested at 18 months after planting. The 50% shading revealed the significantly highest dry rhizome weight per plant specimen 275.41 ± 97.05 g and total phenolic compounds as 38.18 ± 5.38 mg gallic acid equivalent/g dry extract. DBS1 content and EC50 of DPPH radical scavenging capacity were not significantly different among shading treatments as 2.38 ± 1.44 – 3.58 ± 1.91% w/w and 22.63 ± 6.39 – 36.15 ± 14.06 µg/ml, respectively. Based on these results, D. birmanica should be cultivated under 50% shading.